The present invention relates generally to surge protectors, and more particularly, to a surge protector provided with a thermally activated failsafe mechanism for use with, for example, telephone equipment.
Surge protectors are widely used for the protection of equipment from overvoltage conditions that may be caused, for example, by lighting or high voltage line contact. For example, telecommunication lines employ various types of surge protectors, which at a minimum, provide overvoltage protection. This is typically done with at least one protection element that is inserted between a conductive tip element of a surge protector and ground. Likewise, typically at least one protection element is inserted between a conductive ring element of the surge protector and ground. When a hazardous overvoltage is present on a line, the overvoltage protection element, for example a gas tube, changes from a high impedance to a low impedance state. This change of impedance effectively shorts the hazardous overvoltage and its associated overcurrent to ground and away from equipment and/or personnel.
A sustained overvoltage is an overvoltage event that which causes excessive heat when the overvoltage, along with the associated overcurrent, flows through the surge protector and is shorted to ground. For example, a sustained overvoltage can occur where a power line has come in continued contact with a protected telephone line, thereby producing a continuous ionization of the gas tube and the resultant passage of overcurrent through the gas tube to ground. Such overcurrent will in many cases destroy equipment and/or the surge protector.
A failsafe mechanism will remain unaffected when subjected to short and/or less severe overvoltage conditions that the surge protector is intended to handle; however, the failsafe mechanism is intended to permanently short this sustained overvoltage to ground.
One known method of providing a failsafe mechanism in a surge protector is the use of a metal fusible element such as a solder joint. The metal fusible element is designed to melt at a predetermined temperature and short the sustained overvoltage to ground. The use of a metal fusible element as a failsafe mechanism is reliable; however, the metal fusible element method requires multiple components, which makes the metal fusible element relatively expensive.
Another known method of providing a failsafe mechanism is the plastic compressive displacement method. This method requires an electrically conductive spring and a plastic member. The plastic member physically and directly contacts both a portion of a ring side, and/or a portion of a tip side and a ground element of a surge protector to insulate the electrical contact path therebetween. For example, the spring is electrically connected with the tip side and biased towards the plastic member, but cannot make electrical contact to short the tip side to the ground element because the plastic member prevents electrical contact. In other words, the plastic member displaces the spring while physically and directly contacting both the electrical contact point of the spring and the electrical contact point of the ground element. The electrical contact point of the spring is intended to come into electrical contact with the electrical contact point of the ground element if the failsafe mechanism is activated. In operation, as the temperature of the ground element of the surge protector increases due to a sustained overvoltage the plastic member melts allowing the spring to push its way through the plastic member to electrically contact and short the tip side and/or ring side to the ground element. Although, the plastic compressive displacement method is relatively inexpensive, the method is inherently unreliable. The plastic compressive displacement method is inherently unreliable because residual plastic from the melted plastic member can remain between the spring and the intended electrical contact point during the sustained overvoltage condition, thereby interfering with the path to ground. Consequently, telephone equipment and/or personnel can be exposed to hazardous voltages and/or currents because the spring did not properly short to ground.
The present invention is directed towards a surge protector having a failsafe mechanism including at least one overvoltage protection element, at least one arm assembly, at least one ground element, at least one resilient member, wherein the at least one resilient member is electrically connected to the at least one ground element, at least one protrusion operably positioned between the at least one resilient member and the at least one arm assembly, wherein the at least one protrusion is in thermal contact with the at least one resilient member, the at least one protrusion prevents the at least one resilient member from electrically contacting the at least one arm assembly during normal operation, and wherein as a result of a sustained overvoltage condition the temperature of the at least one resilient member increases to soften the at least one protrusion and allow the at least one resilient member to electrically contact the at least one arm assembly and thereby short the at least one arm assembly to the ground element.
The present invention is further directed to a surge protector having a failsafe mechanism including a base, at least one overvoltage protection element, at least one ground element, at least one arm assembly, at least one resilient member, wherein the at least one resilient member is electrically connected to the at least one ground element, at least one protrusion extending from the base, wherein the at least one protrusion is in thermal contact with the at least one resilient member and prevents the at least one resilient member from electrically contacting the at least one arm assembly during normal operation, and wherein as a result of a sustained overvoltage condition the temperature of the at least one resilient member increases thereby softening the at least one protrusion and allowing the at least one resilient member to electrically contact the arm assembly to short the arm assembly to ground.
The present invention is further directed to a surge protector having a failsafe mechanism including a base, the base having a generally planar surface, at least one overvoltage protection element, a ground element, the ground element comprising a ground pin, the ground pin having a collar, at least one arm assembly, a torsional spring, the torsional spring having at least one arm and a coil with an aperture therethrough, wherein the torsional spring is in electrical contact with the ground pin, and the coil of the torsional spring is disposed between the collar of the ground pin and the planar surface of the base, at least one protrusion extending from the planar surface of the base, wherein the at least one protrusion is in thermal contact with the at least one torsional spring and prevents the at least one torsional spring from electrically contacting the at least one arm assembly during normal operation, and wherein as a result of a sustained overvoltage condition the temperature of the at least one arm of the torsional spring increases thereby softening the at least one protrusion and allowing the at least one arm of the torsional spring to electrically contact the arm assembly to short the arm assembly to the ground pin.